RB1 and lip and oral cavity carcinoma: Our meta-analysis on the predictive value of the loss of expression of the pRb tumor suppressor protein, carried out on a total of 6 studies and 330 patients in the early stages of oral carcinogenesis, shows that the loss of pRb expression assessed by immunohistochemical techniques behaves as a significant risk marker for progression to oral cancer in oral leukoplakia (RR = 2.00, 95% CI = 1.22–3.29, p = 0.006).